There are conventional variable power distributors described in, for example, JP 2522201 B and JP 3367735 B. FIG. 13 is a diagram created with reference to those documents and shows a structure of a variable power distributor used for a transmission system. The variable power distributor shown in FIG. 13 includes a first transmission line 1 and a second transmission line 2 as a set of transmission lines. A 90-degree hybrid circuit 3 is provided on an output side of the set of the transmission lines and a 90-degree hybrid circuit 4 is provided on an input side thereof. The 90-degree hybrid circuit 4 in which one of input ends thereof is terminated is a two-way distributor (phases at two output ends are shifted to each other by 90 degrees). A normal two-way distributor may be provided instead of the 90-degree hybrid circuit 4.
A first variable phase shifter 5a, a first variable resistance attenuator 6a, and a power amplifier 7a are provided on the first transmission line 1 between the 90-degree hybrid circuit 4 and the 90-degree hybrid circuit 3. Similarly, a second variable phase shifter 5b, a second variable resistance attenuator 6b, and a power amplifier 7b are provided on the second transmission line 2 between the 90-degree hybrid circuit 4 and the 90-degree hybrid circuit 3.
Next, the operation of the variable power distributor having the above-mentioned structure will be described. An input signal is divided into two to be distributed to two systems of the first transmission line 1 and the second transmission line 2 through the 90-degree hybrid circuit 4 in which the other of the input ends thereof is terminated. An amplitude and a phase of the input signal on each of the transmission lines are subjected to variable control through the variable phase shifter 5a (5b)and the variable resistance attenuator 6a (6b). Power of the signals is amplified by the power amplifier 7a (7b). The signal is distributed through the 90-degree hybrid circuit 3. In general, ends of the 90-degree hybrid circuit 3 are connected to a polarization control antenna, so that the polarization can be arbitrarily set.
In such a variable power distributor, generally, each of components such as the 90-degree hybrid circuits 3 and 4, the variable phase shifters 5a and 5b, the variable resistance attenuators 6a and 6b, and the power amplifiers 7a and 7b normally includes an error. Therefore, in order to perform accurate control, it is considered important to detect an error in each of the components and estimate amplitude and phase correction values to be set based on the detected error.
Note that the variable phase shifters 5a and 5b and the variable resistance attenuators 6a and 6b can arbitrarily change the amplitude and the phase, so the error is not taken into account hereafter.
In the conventional variable power distributor, the components are separately checked to estimate an error in a preliminary step toward building the variable power distributor. Therefore, estimation measurement requires a time multiplied by the number of components, so that an estimation time becomes very long. After the variable power distributor is built, the error in each of the components cannot be estimated, with the result that it is impossible to estimate an error due to an interference between the components which is caused by building the variable power distributor.
As described above, in the case of the conventional variable power distributor, it is difficult to detect the error in each of the components after the variable power distributor is built. Therefore, the components are separately checked to estimate an error before building, which leads to a problem in that the estimation measurement requires the time multiplied by the number of components and thus the estimation time becomes very long. In addition, amplitude and phase set values cannot be corrected after building.
The present invention has been made to solve the above-mentioned problems. An object of the present invention is to obtain a variable power distributor capable of calculating an amplitude ratio and a phase difference as errors between transmission lines of two systems after the variable power distributor is built and correcting the amplitude and phase set values based on the errors, an error detection method thereof, and a set value correction method.